

Class JZA^JLBl 



Book 



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SMITHSONIAN DEPOSIT 



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REPORT 



EXPERIMENTS MADE BY ASSISTANT W. H. HEARDING, 



UPON THE 



Compressive Power of Pine & Hemlock Timber, 



UNDER THE DIRECTION OF 



Major D. C. Houston, Corps of Engineers, U. 8. A., 
February 6, 1871, 



ENGINEER DEPARTMENT, 

1872. 



£ 

£ 
% 



U. S. ENGINEER OFFICE, 

Milwaukee, March 20th, 1871. 



Bri^. General A. A. Humphreys, 

Chief of Engineers, U. S. A.. 
Washington, D. C. 

General : I have the honor to submit a Report by Assist. W. H. 
Hearding on the respective merits of Hemlock and Pine timbers for the 
construction of cribs used in the harbor improvements on the great lakes, 
and {riving some interesting results relating to the strength of crib work. 
He deduces two results of considerable practical importance. First, that 
the bolts used should be headed. Second, that instead of being made 32 
inches long as they now are, and passing through two courses \2 // \\2 // 
timber and 8 inches into the third course, they should, in preference, be 
made only 22 inches in length, passing through but one course, and 10 
inches into the next course. The first result is corroborated by observa- 
tion of cribs that have been broken by the action of storms; in all cases 
the bolts are left standing, the upper timber having been forced off the 
bolts. Fig. A on the Plate shows the condition of two timbers connected 
by bolts L| inch square, driven in a hole bored by a 1 1-16 inch auger, 
according to the practice here. The fibres of the wood are broken as in- 
dicated. Now a comparatively small force only is required to slip the 
upper timber off the bolts. If a wedge is inserted a few blows will do 
this, and in all cases the bolt remains firm in the lower timber. But 
if it be attempted to draw the bolt from the lower timber, it is found 
that a force is required, in case of Hemlock, of 8 Tons upon the 12 in- 
ches of bolt, and in Pine of G Tons. Hence if the bolts are headed, 
there will be required a force of 8 Tons for each bolt, to separate two 
courses of Hemlock timber, in case the bolts are driven 12 inches into 
the lower timber, and for a single course on the side of a 32 foot crib as 
now constructed 96 Tons will be required. 

The importance then of heading the bolts seems unquestionable and 
the expense of this will only be, from estimates furnished by iron manu- 
facturers, or say about six to seven dollars per Crib 32 / X-0 / X17 / (2 cts. 
per bolt). The second conclusion of Mr. Hearding, that the bolts should 
be shortened I do not concur in. The holding powers of a bolt headed 
as suggested, will be greater the farther it is driven, and the force requi- 
red to separate the upper timber from the one below it will be greater in 
case 32-inch bolts are used, than if 20-inch bolts are used as the sketches 
Figs. B and C on the accompanying Plate show. 

Heretofore in Crib construction in this vicinity bolts have been used 
without heads and where Cribs have been broken it seems to have arisen 
from this cause. By omitting heads a large portion of the strength of 



the structure is lost. When Cribs are exposed to Btorme only partially 
filled as frequently happens, they are peculiarly exposed to being separa- 
ted, but if the bolts were headed, the upper timbers would h>- securely 
fastened to the bottom course. 

I have deemed this matter of sufficient importance to be tin- subject of 
a special report, as it is possible that the system adopted h4rc ifl followed 
elsewhere. 

I am, General, very respectfully, 

Your obedient servant, 

1). C. HOUSTON, 

Major Kii'jim 



REPORT 



U. S. Engineer Office, 

Milwaukee, February 6, 1871. 



Major D. C. Houston, 

Corps of Engineers, U. S. A. 



Sir: I respectfully present the following Report upon the experiments 
which I have made for the purpose of elucidating the doubts which have 
•existed in regard to the relative properties of Pine and Hemlock timbers, 
-as they are the kinds most frequently used in the construction of Piers 
for the improvement of the Harbors on the N. & N. W. Lakes. 

Having procured the services of a skilful workman and selected superior 
well seasoned timbers having the same cross-section (12 // X12 // ), I pro- 
ceeded to test their relative compressive powers to hold the bolts which 
constitute the principal bond in the construction of Cribs and other struc- 
tures. 

For experiment No. 1, a block of soft White Pine 4 feet 6 inches in 
length, was placed over a block of Hemlock timber of the same length, 
and a hole was bored with a l|-inch auger through both of the timbers at 
a distance of 18 inches from one extremity of the blocks; a H-inch square 
bolt was then driven into the auger hole until it projected one inch from 
the under side of the Hemlock timber; the bolt used was 32 in. long; so that 
the top portion of it, 7 inches in length, was left standing out above the 
Pine timber. The blocks were then carefully turned over, and a hole was 
bored with the same auger at a distance of 18 inches from the other ex- 
tremity of the blocks, in an opposite direction to the first, through both 
the Hemlock and Pine timbers, and a bolt was driven as before described, 
through both the Hemlock and Pine, until it projected one inch from the 
under side of the Pine block; the space between the centres of the bolts 
was therefore 18 inches. 

Two oak wedges, each 4 inches in width, were then inserted between 
the blocks, one on either side, opposite to each other, and midway from 
the bolts and ends of the blocks. The wedges were struck alternately 
with a mallet, and with as equal a force as could be applied by hand until 
the blocks were separated. 

Result. — The timber nearest the head of the bolt, or the timber which 
was uppermost when the bolt was driven, drew upon the bolt in both 
cases, leaving the lower ends of the bolts projecting from the under sides 
•of the blocks just as they were driven. 



In making Experiment No. 2, the same kinfli of timber were need, 
each stick being 12 feet in Length. At a distance of 2«» inches from one 
of the extremities of the sticks, two holes were bored, one of which vrhen 
the pine was uppermost, from the top surface of the pine, through both 
pine and hemlock, and (vice versa) when the hemlock wa> appem 
before described. 

The centres of the holes were at a distance of four inches from each 
other on the cross-section, and four inches from either side of the timbers; 
1^-inch bolts of 32 inches in length were driven ;is described in the first 
case. A jack-screw was used in making this experiment, by placing it 
in a slot or gain, which was cut into the ends nearest the bolts; the timber* 
were separated by a steady strain of the screw. 

Result. — The upper timbers, or those nearest the heads of the bolts, 
drew upwards, as in the first experiment. 

As the results of these experiments did not determine the point in ques- 
tion, I obtained permission to use one of the Hydraulic presses belong- 
ing to the Milwaukee and St. Paul R. R. Co., hoping thereby to obtain 
definite results. For experiments Nos. 3, 4 and 5, blocks of Timber, each 
3 feet in length, were bolted together in the manner as described for ma- 
king Ex. No. 1, [i. e.), two bolts were used of the same size, driven 
into holes bored at equal distances from the ends, at a distance of one 
foot from each other, with the same auger, and inversely as before de- 
scribed. Ex. No. 3 being made with two blocks of Hemlock. F.x. No. 4, 
with two blocks of soft White Pine, and Ex. No. 5 with two blocks of Nor- 
way pine, in pairs. 

Wedges were inserted between the blocks as in Ex. No. 1, and the 
press power was applied. 

Result. — The power gained through the introduction of the w< 
reduced the duty required directly from the press, so that the direct force 
applied was not sufficient to register the quantity exerted in separating 
the blocks-, but in each case, the top timbers drew on the bolts, leaving 
the lower portion of the bolts unmoved. 

The experiments thus far were of but little service in the elucidation of 
the point in question; but were valuable for reasons which I shall here- 
after state. 

I next applied a direct force from the press, upon an increased power 
of friction, and for the three subsequent experiments the bolts were head- 
ed, so that they should of necessity be drawn from the timber, instead of 
allowing the timber to slide upon the bolts. 

The drawings accompanying this report, exhibit the manner in which 
the bolts were driven, the positions of the timbers, and the method of 
applying the power. 

For making experiments Nos. 6, 7 and 8, the timbers were tut and 
prepared, the holes bored, and the bolts inserted in the same manner for 
each experiment, the timbers in each separate case being homogeneous. 

For Ex. No. 6, Hemlock timber was used, two blocks of which were 
each 2\ feet long; the third was 3 feet in length. The two shorter Mocks 
were laid parallel to each other, at right angles to, and transversely over 
the longer block, their outer sides being upon the same plane with the 
ends of the longer block; it was necessary to place them in this position, 
so as to admit the head of the ram, and that it might pass freely between 



them; the shorter diameter of this machine being eleven inches; two holes 
were bored with 1 1-16-inch auger, in position diagonally across a hori- 
zontal square of one foot at either end of the blocks as shown on the 
drawings, the outer bolts being consequently driven at a distance of but 
4 inches from the ends of the longer timber. The bolts were upset or 
headed symmetrically so that the top «r head of each bolt was increased 
in size £ of an inch; the heads of the bolts were therefore If inches 
square before they were driven, and the impact of the hammer increased 
this size | of an inch more, making them lh inches square after they were 
driven. 

The increased force required to drive them into the diminished size of 
the hole was evident. 

For Ex. No. 7, Soft White Pine timber was prepared and bolted in the 
same manner as for No. 6. 

For making Ex. No. 8, Norway Pine timber was prepared and bolted 
in the same manner as the preceding. 

I may here state that the bolts were driven into both the kinds of Pine 
Timber within a distance of four inches from the ends without splitting 
them. 

From my knowledge of the character of Hemlock timber, I was con- 
fident that a bolt could not be driven as near as 4 inches to the ends with- 
out its splitting; I therefore left the ends of the longer block intact until 
the bolts were driven, and sawed them off to the required length after- 
wards. 

The blocks being thus prepared, they were placed before the press, 
the two shorter blocks being in a horizontal position in front, the longer 
standing vertically in the rear; horizontal struts were placed between the 
short blocks and the Iron backing, which kept them firmly in their posi- 
tion, leaving a play of two inches between the vertical block and the 
backing. The ram was then introduced between the horizontal blocks, 
and brought in contact with the vertical block, thus a direct pushing force 
was applied from the press with the following results, viz: 

For Ex. Nd. 6 with Hemlock timber, a force of 32 Tons was applied 
which drew the bolts, showing the timber to have a compressive power 
of 8 Tons upon 12 inches of the lower end of the bolt. 

For Ex. No. 7 with soft White Pine timber, a force of 20 Tons sepa- 
rated the blocks, but in this case the heads of the bolts were drawn into 
the timber without starting the bolts, furnishing another proof of the 
vastly superior compressive power of the lower over the upper timber, 
and also showing that the heads of the bolts should be increased in size 
for this kind of timber. For Ex. No. 8 with Norway Pine Timber, the 
force iipplied to the separate blocks was 24 Tons, showing the compres- 
sive power of this timber to be 6 Tons upon the lower part of each bolt 
12 inches in length. 

Ex. No. 9 was a test of the strength of Hemlock Timber 12 // X12 // 
square, the distance between bearings being 2 feet 3 inches. 

A pressure of 55 Tons was applied which broke the timber, and at the 
instant of fracture, the indicator receded rapidly on the dial plate. 

Ex. No. 10. — A pressure of 45 Tons broke a block of soft White Pine 
between bearings of 2 feet 3 inches, cross section 12X12 inches. 

Ex. No. 11 on a block of Norway Pine 1^ ,/ X12 // square the distance 



being the same between the bearings, as in the preceding experiment*; 

a pressure of 04 Tons was exerted before the timber broke and tin- indi- 
cator remained stationary for some seconds before receding. 

Before commenting upon the valuable information deduced from these 
tests, I must acknowledge that I have been Bomewbat prejudiced 
the general use of Hemlock timber fur the construction of Cribs; the 

origin of this predjudice was chiefly owing to the fact, that in two 

of disaster which have come under my notice, the cribs were built of this 

material. 

The results of the experiments above described show conclusively that 
the compressive power of this timber is superior to that of Pine, and that 
I have attributed the losses sustained by the Government in these in- 
stances to a wrong source. 

As an offset to this superior quality, I will however state that a rery 
large percentage of Hemlock timber is shaky, and that it will split much 
more easily than Pine from the driving of bolts, and that in 
where large shoulders are cut to tenons, the beveled portion which act- 
as the bond will chip off with a much slighter blow than is required to 
break a similar tenon cut out of Pine timber: I have seen defects in tim- 
ber of this character occasioned by rolling it to its position on tie 
after its being framed. 

The selected Hemlock timber used in these experiments was of a supe- 
rior quality to ninety out of any hundred sticks which I have seen used 
in Government works, and I am yet of the opinion that Hemlock is not a 
suitable timber to be used where bolts are required to be driven ae 
as 12 inches to the ends of timbers. 

I may here add another practical illustration of the manner in which 
timbers slide upwards on bolts, by citing the disasters which occurred at 
the Harbor of Sheboygan, Wisconsin. 

On the 20th day of October 1869, the last of six Cribs was sunk in ex- 
tension of the South pier at that place, The six Cribs were well tilled 
with stone ballast. On the 17th day of November, four weeks after the 
last Crib was sunk, the two outer Cribs, Xos. 5 and G. were broken, and 
their upper parts carried away during a storm. 

On the 2nd of June, 1870, I examined one of these Cribs under very 
favorable circumstances, the lake being calm, and the water very clear, 
the depth of the water over the remaining portion of the Crib was more 
than seven feet, but I could distinctly see several of the bolts which 
were left standing in the timbers, and over which the upper part of the 
crib was lifted by the sea in the manner demonstrated by the experiments. 

A letter received from Mr. J. 0. Thayer, foreman at Sheboygan Har- 
bor, dated June 9, 1870, of which the following is a copy, is also correl- 
ative evidence of the diminished retentive power of upper timbers upon 
bolts. 

"You once remarked that a man should learn something even day. 
If nothing new. old opinions should be either strengthened or weakened 

An incident at the Harbor led me to make an examination, the result 
of which you may find of some use. Watching Bean taking apart the 
old Crib, part Pine and partly Hemlock, I was struck with the great dif- 
ference of holding power of Holts in the two kinds of wood. Between 
two Hemlock sticks, a Maple wedge under each end, with an ordinary 
blow of the sledge time the bolts. A trial was had on a piece where :i 



35-inch bolt passed through two 12-inch Hemlocks and 8-inches into the 
Pine; wedges were put between the pine and hemlock and bolts drew 
through the 24 inches of Hemlock, and did not start in the 8 inches of 
pine. Is not this significant of the value of the two kinds of material 
in this work?" 

Yours, very respectfully, 

J. 0. THAYER. 

To W. H. Hearding, Assistant Engineer. 

In the first case cited by Mr. Thayer, he says "that an ordinary blow 
•of the sledge drew the bolts.^ He should have said that the blow raised 
the timber on the bolts. In the second case it is evident, that if the bolt 
did not draw out of the 8 inches of Pine, which was the lowest timber, 
the two sticks or 24 inches of Hemlock must have slipped upwards upon 
the bolts, in the manner demonstrated through the first experiments. 

By referring to the drawings exemplifying Ex. No. 1, and denoted 
Eigs. 1 & 1 Bis, and which also exemplify the results of the four succeed- 
ing experiments, it will be seen at once that the changed conditions of 
the fibres produced by driving the bolts through the upper timbers, are 
conducive to the sliding or drawing of the timbers upon the bolts in an 
upward direction, by any lifting force applied at the base of the upper 
timbers; and in the case of the lower timbers which receive the lower 
ends of the bolts, the effect of the change is reversed; the fibres in this 
case acting directly against the withdrawal of the bolts. The unvarying 
results of the experiments show conclusively that some means should be 
devised to prevent the upper timbers from thus sliding upwards on the 
bolts, as the accidents which have come under my observation have un- 
doubtedly occurred through this action. No instance of the breaking of 
bolts having occurred to my knowledge. 

The question therefore is : Not, what shall be done to prevent the 
drawing of the bolts from the timbers, but what method shall be adopted 
to prevent the timbers from drawing upon the bolts ? It is easily 
answered, viz : By heading the bolts, inasmuch as the compressive power 
of the lower timber (which I shall designate as the maximum compres- 
sive power) is undoubtedly sufficient to withstand a force applied by 
the action of the water upon the next upper timber when it is pre- 
vented from sliding upwards through the heading of the bolts. But 
this answer may give rise to the following question: — 

"Will this maximum compressive power exerted upon a bolt surface of 
8 inches in the case of 32 inch bolts being used, be sufficient to resist the 
force applied by the water upon two of the next upper timbers, the bolts 
being headed? I beg leave to waive this question for the present, as it is 
thought that a head upon a bolt of this length will change the condition 
of the upper timbers, and by keeping both of them from sliding, that 
they thus become maximum compressive powers; — this is possibly the 
case, as the authority I have consulted on the question is of a high char- 
acter. 

It would undoubtedly be the case, if the object to be attained was the 
preventing of the withdrawal of the bolts; but as the object is to prevent 
the timber from sliding on the bolts, the case is reversed. 

I will respectfully state the ideas which I have entertained in relation 
to the subject, and which at the same time may be entirely erroneous. 



10 

It would seem to me that if such a change is effected as 
through heading the holts, that the power derived thereby is tub 
1a the maximum power of the timber which is exerted upon the Ion 
tremity of the holts, inasmuch as the retaining power of the bead it de- 
pendent upon the. force acting upon the lower extremity of the holt.-. 

If this is the case, would not an increase of this maximum power be 
desirable? By shortening the holts to Lengths of 22 inches and beading 
them, a large increase of this primary maximum power will be obtained. 
The proportional difference will then he, as 22 — : 10 : : 32 — : 8 inches. 

This large difference is however dependent upon the fact aa to whether 
the increased retentive power is actullv imparted to the upper and middle 
timbers enclosing 32-inch bolts, by their being headed: and if so, whether 
the power thus imparted does not impair or reduce the effect of the com- 
pressive power upon the lower portion of the bolt. 

In continuation of this report, I will assume that my ideas concur with 
those of better authority, and that the obvious necessity for heading the 
bolts is fully agreed upon. Such necessity being acknowledged, 1 infer 
therefrom that by increasing the number of heads to bolts, their retentive 
power is increased, this can only be done by shortening the lengths of the 
bolts; and by shortening them and doing away with a middle timber, 
an increased proportional amount of maximum compressive power will 
be obtained as before stated; this principal power being exerted upou the 
length of the bolt which is inserted into the lower timber gives it in prin- 
cipal the same relation to drift bolts, as the nuts and washers sustain to 
screw bolts. 

I have appended tracings of the side of a Crib 50 feet in length and 
27 in height, Fig. 4 of which exhibits the method at present adopted by 
bolting with 32-inch bolts. Fig. 5 exhibits a system of bolting with 22- 
inch bolts. By the present method (which to be more clearly understood 
I shall designate as the old method) what I term the maximum compressive 
power is exerted upon but 20o8 inches of length of the bolts in this side 
of the Crib. By the new method it is exerted upon 3S42 inches, the dif- 
ference in favor of the new being consequently 1754 inches. This gives 
as a result, (allowing the pressure exerted upon 12 inches of bolt to be 6 
Tons as shown by Ex. No. 8) a difference in favor of the new method of 
877 Tons. As a statement of the minimum power exerted by the upper 
timbers would be only conjectural, I will not venture to assume the force 
in Tons which it would exert. The number of inches of bolts acted upon 
by the minimum power of the upper timbers in the old method is 5916. 
In the new it is 4560 inches. 

The weight of the bolts in the new method is 2994 pounds. 

" " " " " " " old method 2851 

Difference of weight in favor of the old method 143 pounds, 

which at 5 cents per pound would give $7.15 in favor of old method over 
new for one side of a Crib of the specified dimensions. The cost of 
heading the bolts would be comparatively small: certainly not more than 
two cents each. 

To theorize at length upon the action of the destructive forces directed 
against Crib Pier structures would be somewhat obtrusive in this report: 
I have however annexed a sketch illustrative of the manner in which 
Cribs are ruptured, and which also exemplifies the comparative impo- 



11 

tence of unheaded bolts to hold down the timbers subjected to such action. 
See Fig. 6. 

My idea of a Crib is, that it is nothing more than a box, which is 
weighed down and sunk by being filled with stone. The stone in reality 
is the principal constituent in the pier; the cribs or boxes enclosing it are 
so used to keep it in a compact symmetrical shape, and for economical 
considerations of space and means. The force of the waves when di- 
rected against the upper portion of the side of a Crib has a tendency to 
turn it over in the direction of the force applied. The axis upon which 
a Crib has a tendency to turn when subjected to such action, is therefore 
situated at the angle of its base diagonally opposite to the point of ap- 
plication. 

The diagonal line drawn in red, the lower extremity of which termi- 
nates at the outer angle of the base, I assume to be the resultant of the 
force of the waves directed against the side of the Crib. I state this un- 
der the assumption that the Crib is constructed upon a close bottom; but 
as the Cribs used in the construction of piers, are for satisfactory reasons, 
built so that the stone shall be permitted to pass through them, an open 
bottom, or grillage work is inserted instead of boxing them in tightly; 
the upper surfaces of the upper or longitudinal grillage timbers are there- 
fore upon a horizontal plane which is two and one half feet above the 
lower sides of the side and end timbers, (all the timbers having a cross 
section of 12X12 inches) and as the weight of the stone chiefly rests upon 
these timbers, rendering them incapable of being moved except by the 
removal of the stone, the plane of their upper surfaces becomes in fact, 
the base of the Crib, and the axis is therefore transferred to the line of 
this base or plane. 

The diagonal line drawn in blue represents the resultant of the force 
which operates upon this axis. 

It is evident then that the jointure of the timbers next, or six inches 
above the upper surface of the grillage timbers on the side from which 
the force is applied is the first point of attack, or the first point liable to 
rupture. If this jointure has sufficient strength, with the additional power 
of resistance imparted to it, through the weight and friction of the prism 
of stone, which rests against the side of .the crib, to resist the force ex- 
erted, the succeeding courses above are subjected in turn to resist the force. 

The configuration of the crib shown in dotted blue lines on the sketch, 
is perhaps an exaggerated exhibition, the side of which is represented as 
having been lifted over the bolts upon its axis in the manner described. 

I wish to express my acknowledgement of indebtedness to Mr. Albert 
Conro for furnishing materials and tools to make the experiments, and to 
Captain R. S. Littlefield for his assistance in the mechanical arrangement 
of the timbers. 

Respectfully submitted by 

Your obedient servant, 

W. H. HEARDING, Assist. Rngineer. 

Appendix to W. II. Heardiny's Report upon Timber. 
Since the foregoing Report was written, I have computed the strength 
of the kinds of timbers experimented upon, using for the purpose coeffi- 
cients given by Emerson, Simpson, Rankin, Haswell, Haslett, &c. The 
results obtained through these authorities differ so widely that I have 
somewhat doubted the accuracy of the force registered by the gauge of 



12 

'die press. I am inclined however to the belief, that the coefficient! 
by these authorities are erroneous. My reason* for thinking bo, arw- 
first, from the statement of the competent machinist who built the press, 
as he says it records the true force exerted in tons by the much in 
secondly, I have consulted with an engineer of ability who has made many 
similar experiments, and the results obtained by him. correspond with 
those obtained through the experiments stated in the foregoing Report. 
The estimated strength of timbers as per these authorities from that ac- 
tually determined by the experiments is so excessive, that the - 
would be worth the trouble of investigation, inasmuch as if the coeffici- 
ents which are in general use are erroneous,, the public should be made 
aware of the fact. If the force recorded by the press used was not ex- 
actly correct, the results will in no wise be affected, for the discrepancy 
if any, is proportional throughout. 

Yery Respectfully, 

Your obedient servant, 

W. H. HEARDIN 



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